build: Make match_byte a proper proc-macro.

Now these are stable. Fix a bunch of warnings that this exposed.

This seems still a valuable optimization from looking at existing
benchmarks.

Author: emilio

Cargo.toml

@@ -9,7 +9,6 @@ repository = "https://github.com/servo/rust-cssparser"
 readme = "README.md"
 keywords = ["css", "syntax", "parser"]
 license = "MPL-2.0"
-build = "build.rs"
 edition = "2018"
 rust-version = "1.63"
 
@@ -35,7 +34,7 @@ proc-macro2 = "1"
 
 [features]
 bench = []
-dummy_match_byte = []
+dummy_match_byte = ["cssparser-macros/dummy_match_byte"]
 
 [workspace]
 members = [".", "./macros", "./procedural-masquerade"]

build.rs

@@ -15,3 +15,6 @@ proc-macro = true
 [dependencies]
 quote = "1"
 syn = {version = "1", features = ["full", "extra-traits"]}
+
+[features]
+dummy_match_byte = []